    {-# LANGUAGE CPP #-}
    {-# LANGUAGE TypeFamilies #-}
    {-# LANGUAGE FlexibleInstances #-}

    --------------------------------------------------------------------------------
    --  See end of this file for licence information.
    --------------------------------------------------------------------------------
    -- |
    --  Module      :  URI
    --  Copyright   :  (c) 2011, 2012 Douglas Burke
    --  License     :  GPL V2
    --
    --  Maintainer  :  Douglas Burke
    --  Stability   :  experimental
    --  Portability :  CPP, TypeFamilies, FlexibleInstances
    --
    --  Support interning URIs.
    --
    --------------------------------------------------------------------------------

    module Data.Interned.URI
           ( InternedURI
           ) where

    import Data.String (IsString(..))
    import Data.Hashable
    import Data.Interned
    import Data.Maybe (fromMaybe)

    import Network.URI

    -- Could look at adding UNPACK statements before the Int component

    -- | An interned URI. The hashing is based on the
    -- reversed URI (as a string).
    data InternedURI = InternedURI !Int !URI

    instance IsString InternedURI where
      fromString = intern .
                   fromMaybe (error "Error: unable to create a URI.") .
                   parseURIReference

    instance Eq InternedURI where
      InternedURI a _ == InternedURI b _ = a == b

    instance Ord InternedURI where
      compare (InternedURI a _) (InternedURI b _) = compare a b

    instance Show InternedURI where
      showsPrec d (InternedURI _ b) = showsPrec d b

    instance Interned InternedURI where
      type Uninterned InternedURI = URI
      data Description InternedURI = DU !URI deriving (Eq) -- DU {-# UNPACK #-} !URI deriving (Eq)
      describe = DU
      identify = InternedURI
    #if MIN_VERSION_intern(0,9,0)
    #else
      identity (InternedURI i _) = i
    #endif
      cache = iuCache

    instance Uninternable InternedURI where
      unintern (InternedURI _ b) = b

    -- Rather than access the URI components, just use the reverse of the
    -- string representation of the URI.
    instance Hashable (Description InternedURI) where
    #if MIN_VERSION_hashable(1,2,0)
    #else
      hash = hashWithSalt 5381 -- use the stringSalt value from Data.Hashable
    #endif
      hashWithSalt salt (DU u) = hashWithSalt salt ((reverse . show) u)

    iuCache :: Cache InternedURI
    iuCache = mkCache
    {-# NOINLINE iuCache #-}

    --------------------------------------------------------------------------------
    --
    --  Copyright (c) 2003, Graham Klyne, 2009 Vasili I Galchin,
    --    2011, 2012 Douglas Burke
    --  All rights reserved.
    --
    --  This file is part of Swish.
    --
    --  Swish is free software; you can redistribute it and/or modify
    --  it under the terms of the GNU General Public License as published by
    --  the Free Software Foundation; either version 2 of the License, or
    --  (at your option) any later version.
    --
    --  Swish is distributed in the hope that it will be useful,
    --  but WITHOUT ANY WARRANTY; without even the implied warranty of
    --  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    --  GNU General Public License for more details.
    --
    --  You should have received a copy of the GNU General Public License
    --  along with Swish; if not, write to:
    --    The Free Software Foundation, Inc.,
    --    59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    --
    --------------------------------------------------------------------------------